"For season two of 'Legends,' we decided that the perfect antagonist for TV's first-ever team of super heroes would be TV's first-ever team of super-villains, recruited from the ranks of Arrow and The Flash's deadliest adversaries," Executive Producer Marc Guggenheim said in a statement. "Being huge fans of the 'Challenge of the Super Friends,' we've come to call this group our 'Legion of Doom.'"

You may recall that Barrowman and Miller signed deals earlier this year to appear across The CW's "Arrow-verse" shows. Letscher, who previously appeared on "The Flash," joins "Legends of Tomorrow" as a series regular, while "Arrow" alum McDonough will be featured in a recurring role.

The roots of the Legion of Doom lie in the 1978-1979 season of the animated "Super Friends," called "Challenge of the Super Friends," which introduced a team of supervillains led by Lex Luthor. Other members included Captain Cold, Brainiac, Gorilla Grodd, The Riddler, Cheetah and Bizarro.

Versions of the Legion subsequently appeared in comic books, video games and in animated form.

The second season of "DC's Legends of Tomorrow" premieres Thursday, Oct. 13, on The CW.